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Response snapshot Oct 27, 2026, 01:26 UTC

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VulnerabilityCVE-2026-75508

GraphQL-core: Denial of service via comment tokens bypassing the parser's max_tokens limit

The parser's `max_tokens` limit — the documented defence against oversized GraphQL documents — did not count comment tokens.

Published Updated

At a glance

Exploited
Not known
Severity
7.5 High (CVSS 3.1)
Chance of exploitation
0.6% in the next 30 days
Sources
2 independent sources

What to do

GitHub lists first patched versions: graphql-core: 3.2.12; graphql-core: 3.3.0rc1. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-r77w-qph3-7vf8 (opens a new tab)

What happened

### Summary

The parser's `max_tokens` limit — the documented defence against oversized GraphQL documents — did not count comment tokens. A document padded with comments could therefore pass a `max_tokens` check of any size while still allocating one `Token` object per comment, all of which stay reachable for the lifetime of the parsed document. A 38 MB comment-padded payload allocated roughly 92 MB of additional resident memory with `max_tokens=5` in force.

### Details

`Lexer.lookahead()` reads tokens one at a time and skips over comments, returning only the first non-comment token. Each skipped comment is nevertheless fully tokenized, allocated as a `Token` object, and linked into the persistent token list via `token.next` / `token.prev` — the chain that powers source-location reporting, and which is retained as long as the document is.

Continue reading

`Parser.advance_lexer()` incremented the token counter only for the tokens the lexer actually returned. Comments were therefore invisible to the accounting, and `max_tokens` bounded only the *non-comment* tokens.

The practical consequence is a gap between what users reasonably believe `max_tokens` protects and what it did protect. The limit was not broken for ordinary documents — real tokens were still capped correctly — so the shortfall was not observable without specifically testing comment padding.

As with the companion issue, the payload compresses extremely well (`# c\n` repeated), so body-size limits and WAF inspection applied to the compressed request do not see its true size, while the framework decompresses it in memory before the parser is reached.

### Proof of concept

```python import gc import resource from graphql import parse

# 100,000 comments, a 5-token query, and max_tokens=5 — accepted. query = "# c\n" * 100_000 + "{ a }" parse(query, max_tokens=5) # no error raised

# Memory amplification. big = "# padding comment used to amplify memory per token\n" * 500_000 + "{ a }" gc.collect() before = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss parse(big, max_tokens=5) # ~38 MB source after = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss print(f"RSS delta: +{(after - before) / 1024:.0f} MB") ```

Measured on GraphQL-core 3.2.8 / CPython 3.12 / Linux x86_64: the 391 KB payload parsed in 127 ms, and the 38.1 MB payload produced an RSS delta of **+92 MB** — about 2.4× the source size, on top of the source string itself.

### Impact

Denial of service through memory exhaustion. A modest number of concurrent requests can push a worker past a typical 256 MB or 512 MB container limit and trigger an OOM kill. No authentication is required, and no data is disclosed or modified.

Depth limiters and complexity analyzers do not help: they run on the AST after parsing has already succeeded, and the document contains only five real tokens.

### Patches

Fixed in **3.2.12** and **3.3.0rc1**.

`Parser.advance_lexer` now counts every token consumed, including the comment tokens the lexer skips between the previously focused token and the new one, and including the advance onto EOF so that trailing comments are covered. `max_tokens` therefore now bounds every `Token` the parser allocates.

Note the behaviour change: **comments now count toward `max_tokens`.** A comment-heavy document that was previously accepted may now be rejected. If you parse documents containing substantial comments — SDL files with documentation comments, for instance — and you set `max_tokens`, you may need to raise the limit. The `token_count` attribute of a parsed document likewise now includes comments.

### Workarounds

If you cannot upgrade, apply a request body-size limit to the **decompressed** body before the document reaches `parse()`.

Such a limit is worth keeping after upgrading as well: `max_tokens` is one guard among several and bounds the token count, not the overall cost of a request.

### References

- GraphQL specification § 2.1.4 — Comments

### Credits

Reported by @BZHunt, who also reviewed the fixes before release. In memory of ZaX, who was the driving force behind this discovery.

Affected package ranges reported by GitHub: graphql-core: >= 3.2.3, < 3.2.12 graphql-core: >= 3.3.0a3, < 3.3.0rc1

Scores and how they were measured

CVSS base severity

7.5

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.6%

Scored Percentile 47.1%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-r77w-qph3-7vf8 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-r77w-qph3-7vf8, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-r77w-qph3-7vf8, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  4. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-r77w-qph3-7vf8, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  5. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-r77w-qph3-7vf8, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  6. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-r77w-qph3-7vf8, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  7. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-r77w-qph3-7vf8, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  8. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-r77w-qph3-7vf8, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  9. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-r77w-qph3-7vf8, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  10. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-r77w-qph3-7vf8, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  11. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-r77w-qph3-7vf8, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  12. Primary source

    NVD CVE-2026-75508 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  13. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  14. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-75508, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 22). GraphQL-core: Denial of service via comment tokens bypassing the parser's max_tokens limit (CVE-2026-75508). https://kevwire.com/record/CVE-2026-75508

MLA

"GraphQL-core: Denial of service via comment tokens bypassing the parser's max_tokens limit (CVE-2026-75508)." KEVWire, 22 Oct. 2026, kevwire.com/record/CVE-2026-75508.

Chicago

KEVWire. "GraphQL-core: Denial of service via comment tokens bypassing the parser's max_tokens limit (CVE-2026-75508)." Last modified October 22, 2026. https://kevwire.com/record/CVE-2026-75508.

Evidence summary (plain text)

GraphQL-core: Denial of service via comment tokens bypassing the parser's max_tokens limit (Oct 22, 2026).
The parser's `max_tokens` limit — the documented defence against oversized GraphQL
documents — did not count comment tokens. A document padded with comments could
therefore pass a `max_tokens` check of any size while still allocating one `Token`
object per comment, all of which stay reachable for the lifetime of the parsed
document. A 38 MB comment-padded payload allocated roughly 92 MB of additional
resident memory with `max_tokens=5` in force.

`Lexer.lookahead()` reads tokens one at a time and skips over comments, returning only
the first non-comment token. Each skipped comment is nevertheless fully tokenized,
allocated as a `Token` object, and linked into the persistent token list via
`token.next` / `token.prev` — the chain that powers source-location reporting, and
which is retained as long as the document is.
CVSS 7.5 (version 3.1; evidence as of Oct 22, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-75508).
EPSS 0.6% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-75508&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-r77w-qph3-7vf8: https://github.com/advisories/GHSA-r77w-qph3-7vf8
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo1MTozMFrOAAf0Mg%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0OToxMlrOAAf0LQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NzoxN1rOAAf0Kg%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NTozNlrOAAf0Jw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NTowNVrOAAf0JQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0Mzo0NVrOAAf0Iw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0MzozMVrOAAf0Ig%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODozNTowMVrOAAZRcw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODozMDoyN1rOAAY_5Q%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODoyOTowNVrOAAfz8g%3D%3D
NVD CVE-2026-75508: https://nvd.nist.gov/vuln/detail/CVE-2026-75508
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?pubStartDate=2026-10-12T13:35:55.142Z&pubEndDate=2026-10-26T13:35:55.142Z&resultsPerPage=500&startIndex=8500
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-75508&date=2026-10-26
Record ID: CVE-2026-75508.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 26, 2026, 19:40 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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